Mr. Hanson said on Thursday that he did not know why the female calf, who lived for a few days during the last weeks of December, had died. The mother, one of only a few dozen of its type of orca, was seen carrying the dead female calf on Wednesday, though might have been doing so for longer.

The calf was born Dec. 24. Observing researchers noted unusual unspecified behaviors by mother and calf that led them to worry for the young whale's health.

An endangered Pacific Northwest orca that carried her dead calf for over two weeks in 2018 is doing so once again following the death of her new calf.